I don't think I'm all that great, but my dad is a professional artist, so I've been exposed to lots of art (and the making thereof). Here's a bit of what I do:
I don't really do a lot of book learning, so I can't help you there... What has been helpful to me is to go out and look at art and experiment. Find things (minis, paintings, architecture, etc) that you like, and see if you can figure out what makes you like them, why they work.
I frequently find a reference picture on the internet, and paint from that (a great example is the horned owl in my entry). If you're just beginning color theory, I'd heartily recommend that you start ignoring the names of colors on the paint pots. GW is particularly bad about mis-naming colors. Stare at everyday objects, and decompose the colors. Hands are particularly great for this... there's probably 50 different shades of colors on mine (blue, green, gray, orange, pink, etc...). After you've spent some time with this, grab your paints and try to match the colors that you see. (If you're using non-toxic paints, you can even try mixing up your skintone, and painting it on your hand to see how close you can get!).
I generally have a bit of an idea what color realm I want things to be in, and frequently have a very clear image in my head. In those cases, I mix up paints until things look right. When I'm at a loss for inspiration, I tend to play around on google image search, until something strikes my fancy.
I'm at work, so I can't answer the rest right now, but if you have other questions, keep them coming!